Method and apparatus for drying agglomerates



July 26, 1966 c. L. AUSTIN ET AL 3,262,213

METHOD AND APPARATUS FOR DRYING AGGLOMERATES Filed April 2 1965 2 Sheets-Sheet 1 A66 LOMERATOR INVENTORS CURTIS L. AUSTIN LEO RICONDA DONALD E. SCHAETZEL BY M ATT NEY July 26, 1966 c. AUSTIN ET AL 3,262,213

METHOD AND APPARATUS FOR DRYING AGGLOMERATES Filed April 2, 1963 2 SheetS -Sheet 2 INVENTORS CURTIS L. AUSTIN LEO RICONDA DONALD E. SCHAETZEL BYM ATTO NEY United States Patent Ofiice 3,262,213 Patented July 26, 1966 3,262,213 METHQI) AND APPARATUS FOR DRYING AGGLOMERATES Curtis L. Austin, Minneapolis, and Donald E. Schaetzel and Leo Riconda, Wayzata, Minn., assignors to General Mills, Inc., a corporation of Delaware Filed Apr. 2, 1963, Ser. No. 270,069 3 Claims. (CI. 3410) This invention relates to a drying method and apparatus and more particularly, to a method and apparatus for drying fragile aggregates or agglomerates.

Recently processes have been devised for instantizing various materials. These processes have a degree of similarity in that particles of the material to be instantized are wetted with water or some other liquid thereby forming a sticky surface on the particle. In some cases it is possible for the agglomerating fluid to provide the stickiness. The particles are then contacted with one another causing them to agglomerate into loosely bound, randomly sized and shaped particles. The drying of these moist and sticky agglomerates presents an unusually difficult problem. Certain batch-type drying operations, such as tray drying, can be employed for small quantities. However, for a large volume continuous operation, for example the instantizing of flour, such batch type operations are impractical and other methods must be employed. Currently available continuous drying methods have not been satisfactory. One of the problems is that many drying methods cause the moist sticky agglomerates to further agglomerate forming undesirably large particles. These large agglomerates are often diflicult to solubilize and disperse when placed in a liquid and they also lend a very unattractive appearance to the product. Similarly, other drying methods cause a break-down of the agglomerates into their original particles or in undesirably small agglomerates. Such a happening obviously defeats the whole purpose of the instantizing operation.

The major cause of these two deficiencies in the drying method is the application of mechanical energy to the agglomerates during the drying process. In many cases, both deficiencies occur at the same time; in other Words, some particles are broken down to undesirably small size while still other particles are agglomerated to an undesirably large size. Because the nature of the agglomerated particle varies considerably depending on what type of material is agglomerated and what substance is used as the agglomerating liquid, it has been found that some drying methods are applicable to certain types of agglomerates but not to others. Water instantized flour and instantized mixtures of flour and shortening present very difiicult drying problems. With such products, the prior art methods are not only deficient in the above respects but are also deficient in that many of the drying methods are not adaptable to the cleanliness standards of the food industry.

It is therefore an object of this invention to provide a new and improved drying process. It is another object of this invention to provide an improved drying method applicable to moist fragile aggregates or agglomerates. It is a further object of this invention to provide an improved drying process which imparts very little mechanical energy to the particles being dried. It is still another object of this invention to provide a novel drying process which causes very little damage to the particles being dried. It is still a further object of this invention to provide a drying process which does not cause the formation of undesirably large agglomerates. It is yet another object of this invention to provide a new and improved drying and separation apparatus. It is yet a further object of this invention to provide a novel separation apparatus. Various other objects and advantages of the present invention will appear hereinafter.

Certain objects of the present invention are accomplished by a process of drying fragile, moist agglomerates which may involve feeding the agglomerates to a drying zone wherein air or gas moves uninterruptedly and vertically downward throughout the entire drying zone, introducing the agglomerates into a drying gas or air stream entering the top of the drying zone, co-currently passing the drying gas and agglomerates downward through the drying zone, and recovering dried agglomerates from the drying zone.

Certain other objects of the present invention are accomplished by a drying and separating apparatus which may include, among other things, a vertical tubular drying chamber in which heated gas or air from a heater is introduced into the top of the chamber together with moist agglomerates. A separating device is located at the foot or exit of the drying chamber to separate the dried agglomerates from the heated gas or air.

In accordance with the present invention, we have found that the process and the apparatus for carrying out the process provides a unique and highly effective method and apparatus for drying moist agglomerates. The agglomerates are able to pass through the system and be dried with a minimum of agitation and impaction. Indeed, they fall freely throughout the entire drying operation and therefore damage to the product is virtually nonexistent.

The invention is better understood with reference to the drawings in Which:

FIGURE 1 is a front schematic diagram illustrating a preferred drying system and apparatu used in the present invention,

FIGURE 2 is a fractional, partially in section of the upper end of the device of FIGURE 1 showing details of the drying system and apparatus where the air and moist agglomerated particles are mixed,

FIGURE 3 is an isometric view of a portion of the device of FIGURE 2,

FIGURE 4 is a sectional view taken generally along and in the direction of lines 4-4 of FIGURE 1, and

FIGURE 5 is a fractional isometric view of a section of a cone shown in FIGURE 2.

- FIGURES 1 and 2 illustrate certain preferred embodiments of the present invention. The invention concerns drying fragile, moist agglomerates which are passed through a drying zone co-currently with a drying gas or air. Individual particles of material to be agglomerated are formed into small moist agglomerates 12 in the agglomerator 10. The agglomerator operates by moistening the particles with water or a similar agglomerating fluid while contacting the particles with one another so that agglomerates are formed. Several suitable devices and methods are known in the art for accomplishing this result.

The moist agglomerates 12 are introduced from the agglomerator into the receiving tube 17. Instead of feeding the moist agglomerates directly as is illustrated, one may also feed the agglomerates to the receiving tube 17 by means of a conveyor belt or some other suitable device. Because of the fragile and sticky nature of the agglomerates it is desirable to feed them directly from the agglomerator into the receiving tube. The moist agglomerates 12 pass from the receiving tube into the inner portion of the air inlet cone 18. Heated air 11 from the air heater 13 flows through the air duct 14 into the plenum chamber 15. The hot air 11 flows through the perforations 20 of the air inlet cone 18 in a downward direction and engages and intimately mixes with the moist agglomerates 12 and carries them intothe drying chamber 21.

The design of the air inlet cone 18 depends a great deal upon the method of feeding the agglomerates 12 into the drying system. Where the agglomerator 10 is mounted directly above the drying chamber 21 so that the particles enter the drying chamber 21 with considerable velocity, the air inlet cone 18 is desirable. The openings in the cone should be at such an angle and of such size to prevent moist agglomerates 12 from sticking to the sides of the air inlet cone 18, or passing through the perforations 20 of the air inlet cone 18 and becoming lodged between the cone and the wall of the drying chamber 21. The openings or perforations 20 are uniformly spaced over the entire surface of cone 18 so that the air enters the cone uniformly from all sides to direct the particles away from the sides of the cone 18. The perforations 20 are provided with baflles or cut at a suitable angle into the wall of cone 18 (see FIG. 5) so that a particle 12 which is moving toward the wall of the cone 18 will be deflected by hot gas or air 11 entering the cone 18 from duct 14. The entrance angle of the air 11 will depend on the direction of flow of the particles 12, the velocity of the particles, the slope of the walls of the cone 18 and the velocity of the air 11. These factors are controlled so that the laminar flow of the hot air and particles 12' does not result. True laminar flow reduces the efliciency of the drying. We have found that air velocities of 3,000 to 5,000 feet per minute are sufficient in most instances to prevent sticking, escape of the agglomerates and efiicient drying. The optimum air fiow rate will necessarily depend upon the force with which the moist agglomerates 12 are introduced into the drying chamber 21.

The drying chamber 21 is a generally vertical tube, preferably of circular cross-section, which is free of baffles and other interruptions so that a free, uninterrupted flow of air is obtained. If the drying chamber contains interruptions, there will be undesirable agitation and moist agglomerates will be further agglomerated to an undesirably large size or broken down into undesirably small particles.

The heated air 11 flows downward in the drying chamber 21 at a speed of about 500-4,000 feet per minute and preferably about LOGO-2,000 feet per minute, while the agglomerates move at a somewhat different velocity due to the additional influence, for example, gravity acting on the aglomerates. The agglomerates might be accelerated above the air velocity by other well known means to attain the velocity differential. It is advantageous to employ as low an air speed as is practical to avoid damaging the particles. High air velocities cause breakage of the agglomerates during drying and low air velocities are not conductive to good drying. There must be some difference in the velocities of the drying air and the agglomerates, however, in order to effectuate eflicient drying of the agglomerates and preferably the agglomerates are moving faster than the air stream. The optimum air velocity will depend greatly on the character of the moist agglomerates 12, the method of heating the moist agglomerates and the air into the dryer, the amount of moisture which is to be removed from the agglomerates, the ratio of the pounds of air per pound of agglomerates fed to the drying chamber, and the distance which the particles fall during the drying. The drying chamber 21 should have a length generally in the range of 200 feet and preferably in the range of 25-100 feet.

When the moist agglomerates 12 encounter the heated air 11 the agglomerates 12 almost immediately assume a temperature very close to the wet bulb temperature of the heated air 11. Depending on the initial and the desired final moisture contents, the drying of many types of agglomerates will occur during the steady state drying period. An explanation of the mechanism of drying is given in Unit Operations by G. G. Brown, et al., John Wiley and Sons, New York, 1950. Assuming that all the drying takes place during the constant rate Period, the temperature of the moist agglomerates 12 remains rela tively constant as they move progressively downward in the drying chamber 21. Because the drying process is essentially adiabatic, the temperature of the heated air 11 decreases throughout the length of the drier in proportion to the amount of drying. The heated air 11 enters the drying chamber 21 at temperatures of up to about 400 F. and preferably from about 250-300 F. The optimum temperature depends upon the moisture content of the moist agglomerates 12, moisture content of the incoming air, the size of the agglomerates, upon the time of travel through the drying chamber 21 and the ratio of solids to The drier exit stream 24 leaves the drying chamber 21 and enters the separation chamber 25. At this point the air temperature is about 100-200" F. and preferably about 150 F. More desirably, the temperature is as close to the product temperature as possible. The product temperature for a typical flour product would be about 120 F. The separation chamber 25 is of greatly enlarged cross section as compared to the cross section of the drying chamber 21. The decreased air velocity in the separation chamber 25 causes the dried agglomerates 26 to settle from the moist air 27 to the bottom of the separation chamber 25. A fluid bed 28 conveys the dried agglomerates 20 through a chute 29 where they are fed to a fluidizer 30 (or some other device) and conveyed to a storage bin (not shown). The moist air 27 is directed to a cyclone 31 where fins 32 are separated from the exit air 33. If desired, some other recovery device may be substituted for the cyclone. The exit air 33 from the cyclone 31 may be conveyed to an intermittent bag filter (not shown) or other similar device for further recovery of fins, or alternatively, the exit air 33 may be discharged without further recovery of the fins.

The removal of the exit air 33 from the systems should be at such a rate so as to maintain the air pressure at the entrance to the drying chamber 21 at a pressure substantially the same as atmospheric pressure. If a large positive or negative pressure is maintained then expensive equipment may be necessary for the introduction of the agglomerates or larger fluctuation of temperatures may result.

FIGURE 4 illustrates details of the fluid bed 28 and is a section generally along the lines 4-4 of FIGURE 1. The chute 29 is made up of a product conveying portion 35 and an air distributing portion 36 separated by a porous cloth 37. Dried agglomerates 20 are suspended on an air stream which passes from the air conveying portion 36 into the product conveying portion 35. This causes the agglomerated particles 26 to be held in suspension much in the manner of a fluid, and the fluidized particles flow downward in the chute 29 under the force of gravity. The action of the fluid bed cools a typical fiour product to about 70 to F. before it leaves the chute 29. Many variations of the construction of the fluid bed are readily apparent, for example, it is possible to have several fluid beds discharging in opposite directions from the separation chamber 25. One method would be to have two fluid beds discharging in opposite directions meeting near the center of the separation chamber forming an inverted letter V. Another possible embodiment would be to have the bottom of the separation chamber 25 shaped like the letter V having both fluid beds feeding to the center of the separation chamber and discharging through a single rotating air lock valve. It is also possible to use other conveying means, such as a screw or bucket conveyor, for removal of the product from the separation chamber 25.

Despite the many advantages of our preferred method of separating the moist air 27 and the dried agglomerates 26, it is also possible to employ other means. A cyclone is exemplary of such means.

The drying chamber 21 should be as nearly vertical as possible. While drying certain types of agglomerates, the chamber may be tilted slightly, but preferably the chamber is vertical.

A wide variety of materials can be dried using the process and apparatus of the present invention. Exemplary of agglomerates which may be dried by the present method and apparatus include flour, starch, egg whites, milk, egg yolks, whole eggs, orange juice, coffee, tea, chocolate drink products, gelatin, pectin, inorganic salts, such as, ammonium sulfate, sodium hexametaphosphate, sodium chloride, silica gel, and gums, such as, guar gum, locust bean gum, gum tragacanth, and gum karaya. A large variety of still other materials will be obvious to those skilled in the art.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

The embodiments of the invention in which an exelusive property or privilege is claimed are defined as follows:

1. A method of drying fragile, moist flour agglomerates which comprises feeding said flour agglomerates into an air stream having a temperature of about 250 to about 400 F., co-currently passing the heated air and flour agglomerates downward through a drying zone wherein flour agglomerates and air move uninterrupted and vertically downward throughout the entire zone and wherein the velocity of movement of said flour agglomerates through the zone is influenced by gravity, feeding the air and flour agglomerates to a separation zone where the speed of the air stream is reduced thereby allowing the dried flour agglomerates to settle out of the air stream, cooling the dried flour agglomerates and then recovering the dried flour agglomerates from said separation zone.

2. A drying and separating apparatus which comprises a vertical tubular drying chamber, a gas heating means, means interconnecting said heating means and the top of said drying chamber for introducing heated gas and moist agglomerates into said drying chamber, said means for introducing including a receiving tube and a perforated, conical chamber interconnecting the top of said drying chamber and said receiving tube, a separation chamber connected to said drying chamber and having a cross-section greater than said drying chamber, means for removing gas from said separation chamber, and means for removing the dried agglomerates from said separation chamber.

3. A drying and separating apparatus which comprises an uninterrupted vertical tubular drying chamber; an air heater; means interconnecting said heater and the top of said drying chamber for introducing heated air and moist agglomerates into the drying chamber; said means for introducing including a receiving tube and a perforated, conical chamber interconnecting the top of said drying chamber and said receiving tube, a separation chamber having an inclined bottom member including porous material, an inlet for the air and moist agglomerates, and an outlet for air and associated with said drying chamber; means for passing gas upwardly through said porous material to fluidize particles contiguous with the bottom member; and means located at the lower end of the inclined bottom member for removing the fluidized particles.

References Cited by the Examiner UNITED STATES PATENTS 205,551 7/1878 Hoifmann 34174 493,225 5/1893 Shamp 34-174 759,527 5/1904 Irwin 34174 992,295 5/1911 Tiemann 34174 1,196,979 9/1916 Randolph 34-174 1,428,526 10/ 1922 Bradley et a1. 2,240,854 5/1941 Peebles. 3,010,215 11/1961 Kayatz 34-168 FOREIGN PATENTS 275,760 8/ 1927 Great Britain.

WILLIAM F. ODEA, Primary Examiner.

NORMAN YUDKOFF, Examiner.

F. E. DRUMMOND, B. L. ADAMS, Assistant Examiners. 

1. A METHOD OF DRYING FRAGILE, MOIST FLOUR AGGLOMERATES WHICH COMPRISES FEEDING SAID FLOUR AGGLOMERATES INTO AN AIR STREAM HAVING A TEMPERATURE OF ABOUT 250 TO ABOUT 400* F., CO-CURRENTLY PASSING THE HEATED AIR AND FLOUR AGGLOMERATES DOWNWARD THROUGH A DRYING ZONE WHEREIN FLOUR AGGLOMERATES AND AIR MOVE UNINTERRUPTED AND VERTICALLY DOWNWARD THROUGHOUT THE ENTIRE ZONE AND WHEREIN THE VELOCITY OF MOVEMENT OF SAID FLOUR AGGLOMERATES THROUGH THE ZONE IS INFLUENCED BY GRAVITY, FEEDING THE AIR AND FLOUR AGGLOMERATES TO A SEPARATION ZONE WHERE THE SPEED OF THE AIR STREAM IS REDUCED THEREBY ALLOWING 